Allen H A, Derrington A M
School of Psychology, University of Nottingham, University Park, Nottingham, UK.
Vision Res. 2000;40(7):735-44. doi: 10.1016/s0042-6989(99)00223-0.
We compared observers' performance in the same complex motion discrimination task using stimuli defined by luminance or by contrast. They were asked to discriminate between a centred expansion pattern, constructed from four patches of outwards motion, and a distorted expansion pattern, constructed with one patch containing inwards motion and three patches containing outwards motion. We measured performance versus duration and found that for luminance-defined patterns, observers were able to discriminate correctly between these patterns in 75% of trials when the stimulus duration was 200 ms. For contrast-defined patterns, observers required over 2 s to reach this level of performance. Observers did not require such long durations to discriminate correctly between the contrast-defined expansion patterns when the patterns contained fewer patches or when the distorted patterns contained more patches of inwards motion. This suggests that observers performed the task by searching for a patch that contained a pattern moving inwards. There was no such effect on performance with the luminance-defined patterns. These results also suggest that contrast-defined patterns are processed too slowly to provide an input to specialised optic flow detectors that guide navigation in real time. Further, the differences in performance may be due to processing delays from sequential processing of the contrast-defined local motion signals.
我们使用由亮度或对比度定义的刺激，比较了观察者在相同复杂运动辨别任务中的表现。他们被要求区分由四个向外运动的斑块构成的居中扩展模式，以及由一个包含向内运动的斑块和三个包含向外运动的斑块构成的扭曲扩展模式。我们测量了表现与持续时间的关系，发现对于由亮度定义的模式，当刺激持续时间为200毫秒时，观察者在75%的试验中能够正确区分这些模式。对于由对比度定义的模式，观察者需要超过2秒才能达到这一表现水平。当模式包含的斑块较少或扭曲模式包含更多向内运动的斑块时，观察者区分由对比度定义的扩展模式并不需要如此长的持续时间。这表明观察者通过寻找包含向内运动模式的斑块来执行任务。对于由亮度定义的模式，表现没有这种影响。这些结果还表明，由对比度定义的模式处理得太慢，无法为实时引导导航的专门光流探测器提供输入。此外，表现上的差异可能是由于对由对比度定义的局部运动信号进行顺序处理时的处理延迟。
